Code
P1026
RENAULT
P — Powertrain
- Glow plugs, cylinders 4/5/6 - circuit malfunction
Views:
UK: 5
EN: 10
RU: 8
AI status
Completed
Completed
100%
Causes
- Open or shorted glow plug(s) on cylinders 4, 5 or 6
- Poor or corroded connector(s) at glow plugs or harness
- Damaged wiring or short to battery/ground in glow plug circuit
- Faulty glow plug relay or fuse
- Faulty glow plug control module / driver inside the ECU
- Intermittent connection due to oil contamination or heat damage
Symptoms
- Hard or extended cold starting, especially in low temperatures
- Longer cranking time or white smoke on start
- Glow-plug or engine management warning lamp illuminated
- Rough idle or misfires during initial warm-up
- Possible diagnostic trouble codes stored for glow/heater circuits
What to check
- Read freeze frame data and full DTC list with a capable scan tool
- Verify battery voltage >= 12.4 V (higher under cranking) before testing
- Visual inspection: harness, connectors, pins and heat/oil damage around cylinders 4–6
- Check glow circuit fuses and relay operation
- Measure resistance of each glow plug (4, 5 and 6) with plugs disconnected
- Check for supply voltage at glow plug feed with relay energized and check ground continuity
Signal parameters
- Typical glow plug resistance: usually low (approx. 0.2–3 ohms) — refer to OEM spec for exact value
- Supply voltage at feed terminal: near battery voltage (11–14 V) when relay active
- Current draw per glow plug: can be several amps (varies by design) — abnormal zero or very high current indicates open or short
- Control signal: PWM or switched feed depending on vehicle; driver should switch/limit current during pre-heat
Diagnostic algorithm
- Connect a diagnostic scanner, record P1026 and any related codes or freeze frame data.
- Verify battery state of charge and perform a quick wiring/connector visual inspection around cylinders 4–6.
- Check glow circuit fuses and operate the glow relay while observing coil and contacts; replace if faulty.
- With ignition off, disconnect each glow plug (4, 5, 6) and measure resistance to engine ground; compare to OEM limits. Replace any open or out-of-spec plugs.
- With connector disconnected, check for battery voltage at the feed terminal when glow system is commanded ON. No feed points to fuse/relay/wiring fault.
- Check continuity from feed terminal to each glow plug connector and from plug grounds to engine ground; repair any breaks or shorts.
- Back-probe driver outputs at glow control module/ECU while commanding glow ON; confirm switching/PWM and expected voltage/current. Absent or abnormal signal suggests module/ECU fault.
- If wiring and glow plugs are good but driver output is faulty, inspect/replace relay/module or consult ECU repair procedures. Clear codes and perform a test start/warm-up to confirm repair.
- If intermittent, perform wiggle tests, heat/cool cycles or use a scope to capture sporadic failures before replacing major components.
Likely causes
- One or more failed glow plugs on cylinders 4–6 (high resistance or open)
- Connector(s) to the glow plugs loose, corroded, or pushed out of the block
- Broken or shorted feed/return wire in the glow plug harness
- Defective relay or blown fuse in the glow circuit
- Faulty glow driver inside the engine ECU or separate glow control module
Fault status
Status
Glow plugs, cylinders 4/5/6 — circuit malfunction detected (P1026). Inspect glow plugs, wiring, fuse/relay and glow driver.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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